The present invention concerns steering a towed implement.
It is known to steer a towed implement in response to turning the towing vehicle relative to a straight-ahead path.
DE-A1-39 19 561 shows a power steering arrangement for a trailer for agricultural and forest products utility vehicles. The steering is performed by a hydraulic cylinder combination including a first double-acting cylinder which is coupled between the towing vehicle and the tongue of the implement, so as to act as a turning sensor, and a second double-acting cylinder coupled for receiving fluid forced from the first cylinder during turning and transferring the resulting motion to a steerable wheel arrangement of the trailer so that the latter better tracks the turning movement of the towing vehicle. In this type of trailer power steering, it is difficult to back up the trailer without any problem.
EP-A1-O 710 601 shows a power steering arrangement for semi-trailer or trailer that includes a hydraulic cylinder combination including a first double-acting cylinder which is coupled so as to extend and retract in response to a turning operation of the towing vehicle with this movement of the first cylinder causing fluid to be coupled to a second double-acting cylinder which steers a set of wheels on the semi-trailer or trailer. The control arrangement is provided with a centering device through which the axle to which the wheels are attached can be brought and locked into a centered or straight-ahead position. For this purpose a pneumatic equalizing cylinder is used which is selectively coupled to a source of pneumatic pressure, the cylinder controlling a pair of toggle-shaped levers whose ends face away from the equalizing cylinder and serve to contact a plate carried by a steering rod so as to bring a hole in the plate into alignment with holes located in a pair of vertically spaced plates fixed to the wheel axle, alignment of the holes for receiving a locking pin occurring when the wheels are straight-ahead.
The problem underlying the invention is seen in the less than optimum performance and the complicated configuration of known steering systems for towed units.
According to the present invention there is provided an improved steering system for towed units, especially for towed implements of harvesting machines, for example.
An object of the invention is to provide a steering system for a towed implement which steers the wheels of the towed implement in accordance with the amount that the towing vehicle turns from a straight-ahead position, the system including a control by which the wheels of the trailing vehicle can be steered independently of the towing vehicle so that the towing vehicle may be operated in reverse.
A more specific object of the invention is to provide a steering system, as set forth in the previous object, wherein it is applied to a trailing vehicle that has an extensible rear section that is supported on steerable wheels, whereby the control is able to place the steerable wheels in a straight-ahead orientation relative to the trailing vehicle so that extension or retraction of the rear section of the towed implement may be done without difficulty.
These and other objects of the invention will be apparent from a reading of the ensuing description together with the appended drawings.